HOpenGL Libraries (GLUT package)ContentsIndex
Graphics.UI.GLUT.Initialization
Portability portable
Stability experimental
Maintainer sven_panne@yahoo.com
Contents
Primary initialization
Setting the initial window geometry
Setting the initial window mode (I)
Setting the initial window mode (II)
Description

Actions beginning with the init prefix are used to initialize GLUT state. The primary initialization routine is init that should only be called exactly once in a GLUT program. No non-init-prefixed GLUT or OpenGL actions should be called before init.

The other init-actions may be called before init. The reason is these actions can be used to set default window initialization state that might be modified by the command processing done in init. For example, initWindowSize (WindowSize 400 400) can be called before init to indicate 400 by 400 is the program's default window size. Setting the initial window size or position before init allows the GLUT program user to specify the initial size or position using command line arguments.

Synopsis
init :: String -> [String] -> IO [String]
initArgs :: IO (String, [String])
data WindowPosition = WindowPosition CInt CInt
initWindowPosition :: WindowPosition -> IO ()
data WindowSize = WindowSize CInt CInt
initWindowSize :: WindowSize -> IO ()
data DisplayMode
= RGBA
| RGB
| Index
| Single
| Double
| Accum
| Alpha
| Depth
| Stencil
| Multisample
| Stereo
| Luminance
initDisplayMode :: [DisplayMode] -> IO ()
data Capability
= RGBA'
| RGB'
| Red
| Green
| Blue
| Index'
| Buffer
| Single'
| Double'
| AccA
| Acc
| Alpha'
| Depth'
| Stencil'
| Samples
| Stereo'
| Luminance'
| Num
| Conformant
| Slow
| Win32PFD
| XVisual
| XStaticGray
| XGrayScale
| XStaticColor
| XPseudoColor
| XTrueColor
| XDirectColor
data Relation
= IsEqualTo
| IsNotEqualTo
| IsLessThan
| IsNotGreaterThan
| IsGreaterThan
| IsAtLeast
| IsNotLessThan
data CapabilityDescription
= Where Capability Relation CInt
| With Capability
initDisplay :: [CapabilityDescription] -> IO ()
Primary initialization
init
:: StringThe program name.
-> [String]The command line arguments
-> IO [String]Non-GLUT command line arguments

Given the program name and command line arguments, initialize the GLUT library and negotiate a session with the window system. During this process, init may cause the termination of the GLUT program with an error message to the user if GLUT cannot be properly initialized. Examples of this situation include the failure to connect to the window system, the lack of window system support for OpenGL, and invalid command line options.

init also processes command line options, but the specific options parsed are window system dependent. Any command line arguments which are not GLUT-specific are returned.

X Implementation Notes: The X Window System specific options parsed by init are as follows:

  • -display DISPLAY: Specify the X server to connect to. If not specified, the value of the DISPLAY environment variable is used.
  • -geometry WxH+X+Y: Determines where windows should be created on the screen. The parameter following -geometry should be formatted as a standard X geometry specification. The effect of using this option is to change the GLUT initial size and initial position the same as if initWindowSize or initWindowPosition were called directly.
  • -iconic: Requests all top-level windows be created in an iconic state.
  • -indirect: Force the use of indirect OpenGL rendering contexts.
  • -direct: Force the use of direct OpenGL rendering contexts (not all GLX implementations support direct rendering contexts). A fatal error is generated if direct rendering is not supported by the OpenGL implementation. If neither -indirect or -direct are used to force a particular behavior, GLUT will attempt to use direct rendering if possible and otherwise fallback to indirect rendering.
  • -gldebug: After processing callbacks and/or events, check if there are any OpenGL errors by calling getError. If an error is reported, print out a warning by looking up the error code with errorString. Using this option is helpful in detecting OpenGL run-time errors.
  • -sync: Enable synchronous X protocol transactions. This option makes it easier to track down potential X protocol errors.
initArgs :: IO (String, [String])
Convenience action: Initialize GLUT, returning the program name and any non-GLUT command line arguments.
Setting the initial window geometry
data WindowPosition
Window position, measured in pixels.
Constructors
WindowPosition CInt CInt
initWindowPosition :: WindowPosition -> IO ()

Set the initial window position. Windows created by createWindow will be requested to be created with the current initial window position. The initial value of the initial window position GLUT state is WindowPosition (-1) (-1). If either the X or Y component of the initial window position is negative, the actual window position is left to the window system to determine.

The intent of the initial window position is to provide a suggestion to the window system for a window's initial position. The window system is not obligated to use this information. Therefore, GLUT programs should not assume the window was created at the specified position.

data WindowSize
Window size, measured in pixels.
Constructors
WindowSize CInt CInt
initWindowSize :: WindowSize -> IO ()

Set the initial window size. Windows created by createWindow will be requested to be created with the current initial window size. The initial value of the initial window size GLUT state is WindowPosition 300 300. The initial window size components must be greater than zero.

The intent of the initial window size is to provide a suggestion to the window system for a window's initial size. The window system is not obligated to use this information. Therefore, GLUT programs should not assume the window was created at the specified size. A GLUT program should use the window's reshape callback to determine the true size of the window.

Setting the initial window mode (I)
data DisplayMode
A single aspect of a window which is to be created, used in conjunction with initDisplayMode.
Constructors
RGBASelect an RGBA mode window. This is the default if neither RGBA nor Index are specified.
RGBAn alias for RGBA.
IndexSelect a color index mode window. This overrides RGBA if it is also specified.
SingleSelect a single buffered window. This is the default if neither Double nor Single are specified.
DoubleSelect a double buffered window. This overrides Single if it is also specified.
AccumSelect a window with an accumulation buffer.
AlphaSelect a window with an alpha component to the color buffer(s).
DepthSelect a window with a depth buffer.
StencilSelect a window with a stencil buffer.
MultisampleSelect a window with multisampling support. If multisampling is not available, a non-multisampling window will automatically be chosen. Note: both the OpenGL client-side and server-side implementations must support the GLX_SAMPLE_SGIS extension for multisampling to be available.
StereoSelect A Stereo Window.
LuminanceSelect a window with a "luminance" color model. This model provides the functionality of OpenGL's RGBA color model, but the green and blue components are not maintained in the frame buffer. Instead each pixel's red component is converted to an index between zero and getNumColormapEntries and looked up in a per-window color map to determine the color of pixels within the window. The initial colormap of Luminance windows is initialized to be a linear gray ramp, but can be modified with GLUT's colormap actions. Implementation Notes: Luminance is not supported on most OpenGL platforms.
Instances
Eq DisplayMode
Ord DisplayMode
Enum DisplayMode
Bounded DisplayMode
initDisplayMode :: [DisplayMode] -> IO ()

Set the initial display mode used when creating top-level windows, subwindows, and overlays to determine the OpenGL display mode for the to-be-created window or overlay.

Note that RGBA selects the RGBA color model, but it does not request any bits of alpha (sometimes called an alpha buffer or destination alpha) be allocated. To request alpha, specify Alpha. The same applies to Luminance.

Setting the initial window mode (II)
data Capability
Capabilities for initDisplay, most of them are extensions of DisplayMode's constructors.
Constructors
RGBA'Number of bits of red, green, blue, and alpha in the RGBA color buffer. Default is "IsAtLeast 1" for red, green, blue, and alpha capabilities, and "IsEqualTo 1" for the RGBA color model capability.
RGB'Number of bits of red, green, and blue in the RGBA color buffer and zero bits of alpha color buffer precision. Default is "IsAtLeast 1" for the red, green, and blue capabilities, and "IsNotLessThan 0" for alpha capability, and "IsEqualTo 1" for the RGBA color model capability.
RedRed color buffer precision in bits. Default is "IsAtLeast 1".
GreenGreen color buffer precision in bits. Default is "IsAtLeast 1".
BlueBlue color buffer precision in bits. Default is "IsAtLeast 1".
Index'Boolean if the color model is color index or not. True is color index. Default is "IsAtLeast 1".
BufferNumber of bits in the color index color buffer. Default is "IsAtLeast 1".
Single'Boolean indicate the color buffer is single buffered. Defaultis "IsEqualTo 1".
Double'Boolean indicating if the color buffer is double buffered. Default is "IsEqualTo 1".
AccARed, green, blue, and alpha accumulation buffer precision in bits. Default is "IsAtLeast 1" for red, green, blue, and alpha capabilities.
AccRed, green, and green accumulation buffer precision in bits and zero bits of alpha accumulation buffer precision. Default is "IsAtLeast 1" for red, green, and blue capabilities, and "IsNotLessThan 0" for the alpha capability.
Alpha'Alpha color buffer precision in bits. Default is "IsAtLeast 1".
Depth'Number of bits of precsion in the depth buffer. Default is "IsAtLeast 12".
Stencil'Number of bits in the stencil buffer. Default is "IsNotLessThan 1".
SamplesIndicates the number of multisamples to use based on GLX's SGIS_multisample extension (for antialiasing). Default is "IsNotGreaterThan 4". This default means that a GLUT application can request multisampling if available by simply specifying "With Samples".
Stereo'Boolean indicating the color buffer is supports OpenGL-style stereo. Default is "IsEqualTo 1".
Luminance'Number of bits of red in the RGBA and zero bits of green, blue (alpha not specified) of color buffer precision. Default is "IsAtLeast 1" for the red capabilitis, and "IsEqualTo 0" for the green and blue capabilities, and "IsEqualTo 1" for the RGBA color model capability, and, for X11, "IsEqualTo 1" for the XStaticGray capability. SGI InfiniteReality (and other future machines) support a 16-bit luminance (single channel) display mode (an additional 16-bit alpha channel can also be requested). The red channel maps to gray scale and green and blue channels are not available. A 16-bit precision luminance display mode is often appropriate for medical imaging applications. Do not expect many machines to support extended precision luminance display modes.
NumA special capability name indicating where the value represents the Nth frame buffer configuration matching the description string. When not specified, initDisplayString also returns the first (best matching) configuration. Num requires a relation and numeric value.
ConformantBoolean indicating if the frame buffer configuration is conformant or not. Conformance information is based on GLX's EXT_visual_rating extension if supported. If the extension is not supported, all visuals are assumed conformant. Default is "IsEqualTo 1".
SlowBoolean indicating if the frame buffer configuration is slow or not. Slowness information is based on GLX's EXT_visual_rating extension if supported. If the extension is not supported, all visuals are assumed fast. Note that slowness is a relative designation relative to other frame buffer configurations available. The intent of the slow capability is to help programs avoid frame buffer configurations that are slower (but perhaps higher precision) for the current machine. Default is "IsAtLeast 0". This default means that slow visuals are used in preference to fast visuals, but fast visuals will still be allowed.
Win32PFDOnly recognized on GLUT implementations for Win32, this capability name matches the Win32 Pixel Format Descriptor by number. Win32PFD can only be used with Where.
XVisualOnly recongized on GLUT implementations for the X Window System, this capability name matches the X visual ID by number. XVisual requires a relation and numeric value.
XStaticGrayOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type StaticGray. Default is "IsEqualTo 1".
XGrayScaleOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type GrayScale. Default is "IsEqualTo 1".
XStaticColorOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type StaticColor. Default is "IsEqualTo 1".
XPseudoColorOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type PsuedoColor. Default is "IsEqualTo 1".
XTrueColorOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type TrueColor. Default is "IsEqualTo 1".
XDirectColorOnly recongized on GLUT implementations for the X Window System, boolean indicating if the frame buffer configuration's X visual is of type DirectColor. Default is "IsEqualTo 1".
Instances
Eq Capability
Ord Capability
data Relation
Relation between a Capability and a numeric value.
Constructors
IsEqualToEqual.
IsNotEqualToNot equal.
IsLessThanLess than and preferring larger difference (the least is best).
IsNotGreaterThanLess than or equal and preferring larger difference (the least is best).
IsGreaterThanGreater than and preferring larger differences (the most is best).
IsAtLeastGreater than or equal and preferring more instead of less. This relation is useful for allocating resources like color precision or depth buffer precision where the maximum precision is generally preferred. Contrast with IsNotLessThan relation.
IsNotLessThanGreater than or equal but preferring less instead of more. This relation is useful for allocating resources such as stencil bits or auxillary color buffers where you would rather not over-allocate.
Instances
Eq Relation
Ord Relation
data CapabilityDescription
A single capability description for initDisplay.
Constructors
Where Capability Relation CIntA description of a capability with a specific relation to a numeric value.
With CapabilityWhen the relation and numeric value are not specified, each capability has a different default, see the different constructors of Capability.
Instances
Eq CapabilityDescription
Ord CapabilityDescription
initDisplay :: [CapabilityDescription] -> IO ()

Set the initial display mode used when creating top-level windows, subwindows, and overlays to determine the OpenGL display mode for the to-be-created window or overlay. It is described by a list of zero or more capability descriptions, which are translated into a set of criteria used to select the appropriate frame buffer configuration. The criteria are matched in strict left to right order of precdence. That is, the first specified criterion (leftmost) takes precedence over the later criteria for non-exact criteria (IsGreaterThan, IsLessThan, etc.). Exact criteria (IsEqualTo, IsNotEqualTo) must match exactly so precedence is not relevant.

Unspecified capability descriptions will result in unspecified criteria being generated. These unspecified criteria help initDisplay behave sensibly with terse display mode descriptions.

Here is an example using initDisplay:

initDisplay [ With  RGB',
Where Depth' IsAtLeast 16,
With  Samples,
Where Stencil' IsNotLessThan 2,
With  Double' ]

The above call requests a window with an RGBA color model (but requesting no bits of alpha), a depth buffer with at least 16 bits of precision but preferring more, multisampling if available, at least 2 bits of stencil (favoring less stencil to more as long as 2 bits are available), and double buffering.

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